Multiple spindle heads for drilling and like machines

ABSTRACT

A MULTIPLE SPINDLE HEAD FOR A DRILLING MACHINE COMPRISES A CARRIER, A PLURALITY OF SPINDLES ROTATABLE IN BEARINGS IN THE CARRIER, EACH SPINDLE HAVING AN ECCENTRIC CRACK PIN AND THE CRANK PINS ENGAGING A DRIVE MEMBER CAPABLE OF GYRATORY MOVEMENT RELATIVELY TO THE CARRIER AND ABOUT AN AXIS PARALLEL TO THE AXES OF THE SPINDLES, IN SUCH A MANNER AS TO ROTATE THE SPINDLES. EACH CRANK PIN IS COUPLED TO THE SPINDLE BY A CRANK PORTION THE AXIS OF WHICH IS INCLINED AT AN ANGLE $ OF LESS THAN 90* TO THE AXIS OF THE SPINDLE, AND THE SPACING OF AT LEAST SOME OF THE SPINDLES IS SUCH THAT THE CRANK PORTIONS OF ADJACENT SPINDLES ARE INTERLEAVED. THE DRIVE MEMBER IS ROTATIONALLY BALANCED BY A BALANCING MEMBER ARRANGED TO GYRATE 180* OUT OF PHASE WITH THE DRIVE MEMBER, THE TWO MEMBERS HAVING BEARING SURFACES ONE OF WHICH ENGAGES AND ROLLS AROUND THE OTHER, IN EPICYCLIC FASHION, AS THE TWO MEMBERS GYRATE.

Sept. 20, 1971 c. K. FITCH ETAL 3,606,559

MULTIPLE SPINDLE HEADS FOR DRILLING AND LIKE MACHINES Filed July 8, 1969 6 Sheets-Sheet 1 rzabZia.

mMM-M 6 Sheets-Sheet 2 f inc.

0 $344 WWW Sept. 20, 1.971 c. K. FITCH E AL MULTIPLE SPINDLE HEADS FOR DRILLING AND LIKE MACHINES Filed July 8, 1969 p n n H Sept. 20, 1.971

FIT EI'AL 3,506,559

MULTIPLE SPINDLE HEADS FOR DRILLING AND LIKE MACHINES Filed July 8, 1969 6 Sheets-Sheet 5 Sept. 20, 1.971

C K- FITCH ET AL MULTIPLE SPINDLE HEADS FOR DRILLING AND LIKE MACHINES Filed July 8, 1969 Sheets-Sheet 4.

l I /V//X/ X/X/X/X/ SebfTZQfI QH 3. K. FITCH ETAL 3,606,559

MULTIPLE SPINDLE HEADS FOR DRILLING AND LIKE MACHINES Filed July 8, 1969 6 Sheets-Sheet 5 i uxp zli1 [$41 if 2 W Sept. 2 0, 19-71 n- El AL 3,50559 MULTIPLE SPINDLE HEADS FOR DRILLING AND LIKE MACHINES Filed July 8, 1969 6 Sheets-Sheet 6 United Smtes Patent 3,606,559 MULTIPLE SPINDLE HEADS FOR DRILLING AND LIKE MACHINES Clifford Kingsbury Fitch, Ditchling, Sussex, and David Henry Hemming, Laughton, England, assignors to Kingsbury Fitch (Developments) Limited, London, England Filed July 8, 1969, Ser. No. 839,903 Claims priority, application Great Britain, May 7, 1969, 23,387/ 69 Int. Cl. B23b 39/16 U.S. Cl. 40853 9 Claims ABSTRACT OF THE DISCLOSURE A multiple spindle head for a drilling machine comprises a carrier, a plurality of spindles rotatable in bearings in the carrier, each spindle having an eccentric crank pin and the crank pins engaging a drive member capable of gyratory movement relatively to the carrier and about an axis parallel to the axes of the spindles, in such a manner as to rotate the spindles. Each crank pin is coupled to the spindle by a crank portion the axis of which is inclined at an angle of less than 90 to the axis of the spindle, and the spacing of at least some of the spindles is such that the crank portions of adjacent spindles are interleaved.

The drive member is rotationally balanced by a balancing member arranged to gyrate 180 out of phase with the drive member, the two members having bearing surfaces one of which engages and rolls around the other, in epicyclic fashion, as the two members gyrate.

The invention relates to multiple spindle heads for drilling and like machines and of the kind comprising a carrier, a plurality of spindles rotatable in bearings in the carrier, each spindle having an eccentric crank pin and the crank pins engaging a drive member capable of gyratory movement, relatively to the carrier and about an axis parallel to the axes of the spindles, in such a manner as to rotate the spindles.

Such known arrangements enable a drive to be transmitted to a multiplicity of spindles which are very closely spaced. However in previously known arrangements the minimum spacing apart of the spindles has been limited by the throw of the crank pin and it is an object of the invention to provide an improved arrangement whereby the minimum spacing apart of the spindles may be reduced.

According to the invention there is provided a multiple spindle head of the kind first referred to wherein each crank pin is coupled to the spindle by a crank portion the axis of which is inclined at an angle 0 of less than 90 to the axis of the spindle, and wherein the spacing of at least some of the spindles is such that the crank portions of adjacent spindles are interleaved as hereinafter defined.

In this specification the crank portions of adjacent spindles are said to be interleaved if the pitch P between the axes of the spindles is less than the radius of throw R of the crank portions plus the diameter D of i a spindle, the pitch however being not less than Dsec 0 (where 6 is the aforesaid angle between the axis of the the crank portion and the axis of the spindle) to prevent interference between the adjacent spindles.

The specific embodiment described in Specification No. 31581/68 includes an arrangement for rotationally balancing the gyrating drive member by a balancing member arranged to gyrate 180 out of phase with the drive member. It will be appreciated that in such an arrangement two opposing centrifugal forces are produced in the drive member and balancing member. In the earlier arrangement these centrifugal forces were borne by the bearings of the drive shaft and by four supporting shafts of the drive member. It is found in practice that this tends to limit the maximum speed of operation of the machine. This is because an increase in speed results in increased centrifugal loads which require bigger bearings to hear them, but bigger bearings themselves increase the rotating weight and therefore add to'the centrifugal loads. The size of the bearings required therefore increases disproportionately with increase of speed and a maximum practical size is soon reached. The present invention, in another of its aspects, sets out to provid means for containing these centrifugal loads. 4-.

According to a second aspect of the'invention, therefore, there is provided a multiple spindle head of the kind first referred to wherein the drive member is rotationally balanced by a balancing member arranged to gyrate out of phase with the drive member, each member having coaxial therewith a circular and axially extending bearing surface, the radii of the two surfaces being such that one surface engages and rolls around the other, in epicyclic fashion, as the two members gyrate.

It will be appreciated that in such an arrangement the centrifugal forces due to the drive member and the balancing member act in opposition at the location where the bearing surfaces engage and tend to cancel one another out.

Preferably one surface is inwardly facing and encircles the other surface which faces outwardly.

The internal surface may be on the drive member and the external surface on the balancing member.

The drive member may be arranged to be gyrated by a shaft rotatable about a fixed axis and having an eccentric portion rotatable in a bearing on the drive member. In this case the balancing member may be gyrated by a further eccentric portion on the same shaft which further eccentric portion is rotatable in a bearing on the balancing member, the two eccentric portions being displaced from on another by 180. 7

Since such an arrangement contains centrifugal loads it will be appreciated that it may not be necessary for supporting means for the drive member to include bearings to carry such loads and thus the speeds of rotation of the drive member can be higher being no longer limited by bearings. However it is still necessary to provide means for preventing rotation of the drive member while it is gyrating and according to another aspect of the invention there are provided such means which need not absorb a great deal of power and which may permit high rotational speeds to be achieved.

According to a further aspect of the invention, there fore, in a multiple spindle head of the kind first referred to there are provided means for preventing rotation of the drive member while it is gyrating, which means comprise one or more intermediate members connecting the drive member to said carrier, each intermediate member being restrained for movement relatively to the carrier in one direction only, normal to the axis gyration, and restrained for movement relatively to the drive member in a direction at right angles to said one direction.

ljreferably ball or roller linear bearings are provided to permit movement of the intermediate member in the two said directions. For example the intermediate member may have a first groove which registers with a groove on the carrier, the two registering grooves locating a plurality of balls between them, and a second groove, at right angles to the first groove, which second groove registers with a groove on the drive member, the two registering grooves locating a plurality of balls between them. There may be provided a plurality of parallel grooves on the carrier and on the drive member, registering with corresponding grooves on the'intermediate member.

Further aspects of the invention will become clear from the following more detailed description of one embodiment of the invention reference being made to the accompanying drawings in which:

FIG. 1 is a section through a multiple spindle drilling machine;

FIG. 2 is a plan view of the machine;

FIG. 3 is an enlarged view showing two adjacent spindles in the machine;

FIG. 4 is a vertical section through an alternative and preferred form of multiple spindle drilling machine;

FIG. 5 is a horizontal section on the line 55 of FIG. 4;

' FIG. 6 is'a diagrammatic exploded isometric view of the linear bearing system for the drive member of the machine of FIGS. 4 and 5;

- FIG. 7 is a vertical section through part of a drill spindle showing the method of connecting a drill to the spindle; and

FIG. 8 is a vertical section through a spindle mounting showing a method of cooling the spindle bearing.

1 Referring to the arrangement shown in FIGS. 1 to 3: the drilling head comprises a main frame 10 integrally formed with cooling fins 11.

A drill support plate 12 which constitutes the aforementioned carrier is bolted across the bottom of the frame 10 and the frame is formed with an internal horizontal wall 13 spaced above the drill support plate 12.

Four upwardly extending pillars 14 are integrally formed adjacent the four corners of the wall 13. A driving shaft 15 is rotatable in bearings 16 in a vertical bore in each pillar 14. A sprocket wheel 17 is secured to the upper end of each shaft 15 and the lower part of each shaft 15, where it projects into the space between the drill support plate and wall 13, is formed with an upper eccentric portion 18 and a lower eccentric pin 19 having their central axes'diametrically opposed with respect to the central axis of the shaft. Each pin 19 engages within a bearing hole adjacent a corner of a rectangular plate 20 which constitutes the aforementioned drive member. The

eccentric portions 18 similarly engage holes adjacent the wheels 17 and large wheel 22 so that when the Wheel 22 I is driven the wheels 17 all rotate in the same direction in "synchronism. Alternatively the motor spindle 23 may .drive the shafts 15 in synchronism through a suitable gear .train, or any other suitable mechanism may be employed to impart gyratory movement to the plate 20 independently of the drill spindles referred to below.

Due to the eccentricity of the pins 19, rotation of the spindles 15 causes the drive plate 20 to gyrate relatively to the support plate 12. Since, as mentioned above, the eccentricity of each portion 18 is opposed to the eccentricity of the pin 19, the plate 21 gyrates 180 out of phase with the plate 20 to act as a counter-balance weight.

A plurality of drill spindles 25 are mounted in plain bearings in the support plate 12. As shown in greater detail in FIG. 3, each spindle 25 is connected by a cranked portion 27 to an upper portion 28 which is received in a plain bearing in the gyrating plate 20. The lower end of each spindle 25 is either formed with a drill head (for example a spade point) or is shaped to receive a detachable drill head, for example by means of a morse taper. The throw of the crank portion of each spindle 25 is such that as the member 20 gyrates the drill spindles are rotated. Beneath the plate 12 is disposed a bed plate 26 mounted on a movable support 29 which is movable in an up and down direction to bri g a workpiece 30 into and out of engagement with the drills. A dust extracting and cooling conduit 31 leads from the side of the frame 10 adjacent the drills.

The workpiece 28 may be a printed circuit board (or a stack of such boards) in which it is required to drill a multiplicity of holes at least some of which will normally be very close to one another. The arrangement shown is such that the crank portions 27 of adjacent spindles are interleaved as they rotate as indicated in FIGS. 1 and 3, so as to give a very close spacing of the drills.

The spindles 25 may be arranged in a required predetermined pattern in the plate 12 (there being a similar pattern of bearing holes in the plate 20) according to the arrangement of holes required in the workpiece. In this case the pattern may be changed by replacing the plates 20 and 12 by plates carrying a different pattern of drill spindles.

Alternatively the plates 12 and 20 may carry an overall grid pattern of bearing holes into which drill spindles may be inserted as required. Alternatively, in the case where the drill spindles are provided with removable tips, there may be provided a complete grid pattern of drill spindles permanently mounted in the support plate 12 and drill tips may be secured to certain spindles according to the pattern of holes required.

Also, providing all drills have the same crank throw, various diameter drill spindles may be used according to the required diameter and spacing of the drills.

In such arrangements there may be provided a plurality of alternative support plates 12 and gyrating plates 20 having spindles mounted in them at different pitches so that plates having the appropriate pitch may be selected according to the pitch of holes required. Both the support plate 12 and gyratory member 20 may, for example, be drilled to form a rectangular lattice of holes at say of an inch pitch in both directions. It will be appreciated that a single set of plates will enable a great variety of patterns of holes to be drilled.

It will be appreciated that the above arrangement enables a multiplicity of holes to be drilled in a single workpiece at a single stroke. This ensures that the holes are precisely located with respect to one another and that no holes are missed which may occur if the holes are drilled one or a few at a time.

FIGS. 4, 5 and 6 show an alternative and preferred form of drilling machine. Referring to FIGS. 4 and 5, the machine comprises a main frame integrally formed with cooling fins 41. A drill carrier assembly 42 is secured across the bottom of the frame 40 and the frame is formed with an internal horizontal wall 43 spaced above the assembly 42.

A driving assembly indicated generally at 44 is mounted on the assembly 42 by three bearing devices 45 arranged to permit gyratory movement of the assembly 44 but to prevent rotation of that assembly.

As best shown diagrammatically in FIG. 6 each hearing device 45 comprises a rectangular lower member 46 fixedly mounted on the upper plate 47 of the carrier assembly 42. The member 46 is formed with a V-sectioned groove 48 in which are received a number of balls 49, which may be formed from tungsten carbide. The balls 49 are also received in a corresponding V-sectioned groove 50 on the underside of a rectangular intermediate member 51. The upper surface of the intermediate member 51 is provided with a V-sectioned groove 52 arranged at right angles to the groove 50. Further balls 53 are received in the groove 52 and also within a registering groove 54 on the underside of an upper member 55. The member 55 is fixedly mounted on a drive plate 56 forming part of the driving assembly 44. Cages (not shown) are provided to locate the balls 49 and 53 in their grooves. Although the members 46 and 55 are each shown as having only one groove, it will be appreciated that each member may, if required, be formed with a plurality of parallel grooves each registering with a corresponding groove on the intermediate member 51.

As best seen in FIG. three of the devices 45 are provided and it will be appreciated that these devices permit low friction movement of the driving assembly 44 relatively to the carrier assembly in two directions at right angles (and hence permit gyratory movement) but prevent rotation of the assembly 44 in the machine.

Gyratory movement is imparted to the assembly 44 by a central driving shaft 57 mounted in bearings 58 and 59 in the machine frame. The shaft 57 is formed at its lower end with a circular cross section eccentric portion 60 which is received in a bearing 61 in an upstanding boss 62 on an upper plate 63 forming part of the driving assembly 44. -It will be appreciated that as the shaft 57 is rotated the eccentric portion 60 will cause the whole as sembly 44 to gyrate.

As in the first arrangement described above, a plurality of drill spindles of the kind described with reference to FIG. 3 are mounted in plain hearings in the carrier assembly 42. The lower end of each spindle has secured thereto a drill in a manner described below. The throw of the crank portion of each spindle is the same as the throw of the eccentric portion 60 of the shaft 57 so that as the assembly 44 is gyrated the drill spindles rotate. Beneath the carrier assembly 42 is disposed a bed plate (not shown) mounted for movement up and down to bring a workpiece into and out of engagement with the drills.

To absorb the upward axial thrust on the driving assembly 44 during drilling there are provided four air bearing assemblies indicated generally at 67.

As best seen in FIG. 4 each air bearing assembly comprises a pillar 68 integrally formed in the wall 43 and projecting downwardly towards the driving assembly 44-. Received within the pillar 68 is a bush 69 having a central air passage 70 which is in communication, via union 71, with a source of air under pressure. The lower end of the passage 70 opens out into a circular shallow recess 72 over which is secured a bearing plate 73 formed with a plurality of holes 74. The lower surface of the bearing plate 73 is disposed closely adjacent the fiat upper surface of a circular upstanding portion 75 of the plate 63. During operation of the machine air is supplied under pressure through the passage 70, passes through the holes 74 and provides an air bearing between the plate 73 and surface 75.

To balance the gyrating assembly 44 there is provided a circular balancing member 76 having a central bearing 77 which is engaged by an eccentric portion 60a formed on the shaft 57 above the portion 60. The two eccentric portions 60 and 60a are displaced from one another by 180 and the mass of the member 76 is chosen so that the centrifugal force resulting from its rotation is substantially equal and opposite to the centrifugal force due to the rotation of the driving assembly 44.

The balancing member 76 is formed with a downwardly projecting peripheral skirt 78 which provides an outward- 1y facing axial bearing surface 79. The skirt 78 is disposed within an upstanding wall 80 formed on the plate 63, the inner surface of which wall has secured to it an annular bearing ring 81 providing an inwardly facing bearing surface 82. The diameters of the bearing surfaces 79 and 82 are so chosen that the balancing member 76 rolls around inside the wall 80 in epicyclic fashion (as best seen in FIG. 5) so that the opposing centrifugal forces on the balancing member 76 and assembly 44 tend to cancel each other out at the location where the two bearing surfaces 79 and 82 engage.

A counterweight 83 is mounted on the shaft 57 to rotate with it for the purpose of dynamic balancing of the rotating assemblies. However in an alternative arrangement, not shown, the bearing 77 for the balancing member may be disposed below the bearing 61 for the driving assembly and in this case it may be possible to achieve dynamic balancing without the necessity of attaching a further counterweight to the shaft 57.

Although the spindles have been described as having been mounted in plain bearings in the assemblies 44 and 42, air bearings may be provided if required. In the case of air bearings for mounting the spindle crankpins in the drive plate 56, air may be supplied to this plate through central registering apertures in the parts 73 and 75 through which apertures air under pressure passes to the gyrating assembly.

FIG. 7 shows an arrangement by which a drill may be readily attached to a drill spindle. As described in relation to the earlier arrangement a maximum number of drill spindles may be permanently mounted on the machine and a particular pattern of holes may be achieved by fitting drills to the appropriate spindles. As shown in FIG. 7 this may be readily achieved by forming the lower end of each drill spindle 64 with an inclined face 84 formed with a shoulder 85. The upper end of each drill 86 is formed with a matching plane 87 and shoulder 88. To fit the drill 86 to the spindle 64, a sleeve 89 is fitted over the upper end of the drill 86 and the lower end of the spindle 64 is wedged into engagement with the upper end of the drill, within the sleeve 89, as shown in FIG. 7. It is found that this enables drills to be easily fitted to densely spaced spindles. Since a very tight fit is required it may be necessary to slit the sleeve 89 to remove the drill when it is required to change the drill pattern.

When drilling multiple holes at very close pitches the method of attaching the drill to the drill spindle has to be such that it does not impose a limit on the pitch. It is also important that an individual drill can be removed from or attached to a spindle which is in a cluster of drills in close proximity. The method described fulfills this condition and has the added advantage that it is cheap to produce and can be made using tungsten carbide drills. This is important since the invention is particularly applicable to drilling printed circuit boards and it is standard practice to use tungsten carbide drills for this purpose.

To provide quickly changeable drill patterns the machine may be provided with a plurality of drive and carrier assembles. As seen in FIG. 4 the assembly 44 is separable from the bearing 61 at the conical surface 90. Thus to change the drill pattern it is only necessary to detach the carrier assembly 42 from the frame 40 and lower the assemblies 42 and 44 away, and replace them by assemblies having a different drill pattern. The removed assemblies can be taken to another location for changing the drill pattern if required and the working of the machine is interrupted for the minimum amount of time.

As mentioned earlier, an important feature of the invention is the interleaving of the crank portions of adjacent spindles and FIG. 3 shows two adjacent spindles having interleaved crank portions. As mentioned earlier the crank portions of adjacent spindles are said to be interleaved when the pitch P between adjacent spindles is less than the radius of throw R of the crank portions plus the diameter D of a spindle. When this condition exists it is also necessary, to prevent interference between adjacent spindles, for the pitch to be not less than D sec 6 where 0 is the angle shown between the axes of the crank portion 27 and spindle 25. In any arrangement having cranked drill spindles the pressure in the spindle bearing is inversely proportional to the crank thrown, for a given driving torque. An advantage to be obtained by interleaving the crank portions in accordance with the present invention is that for a given driving torque of the spindles the radius of throw R of the cranks is not limited by the pitch of the spindles and can be made sufficiently large to give an acceptable bearing pressure irrespective of the close pitch of the spindles.

In either of the arrangements described above, instead of the upper portion 28 of each spindle being integrally formed with the crank portion 27 as shown in FIG. 3, the crank portion may be formed in its upper part with a conical depression which is engaged by a conical depression in a separately formed portion mounted in the gyrating member 20 or 56.

The supporting plate 12 or carrier assembly 42 are preferably formed from a suitable self lubricating bearing material such as an oil impregnated porous brass, or sintered bronze bearing material, which enables the spacing of the drill spindles to be reduced. The gyratory member 20 or 56 may be made of the same material.

The pitch between holes drilled by the machine may be affected by a temperature change of the spindle bearing plates and it is therefore important that these are maintained at a substantially constant temperature. FIG. 8 shows an arrangement by means of which the spindle bearings may be cooled. Extending vertically between the upper and lower plates of the carrier assembly 42 is a thin-walled stainless-steel bearing tube 91 the upper and lower ends of which are in fluid tight engagement with the plates. The spindle 25 is rotatable in the bearing tube 91 and liquid coolant is circulated between the upper and lower plates and around the bearing tubes. The upper surface of the upper plate is cooled by air from forced draught cooling air provided for the integral drive motor of the machine. This air also cools the driving assembly 44 and the counterbalancing assembly. The under surface of the lower plate of the carrier assembly is cooled by air circulating as a result of the suction employed for swarf removal.

We claim:

1. A multiple spindle head for a drilling machine comprising a carrier, a plurality of spindles rotatable in bearings in the carrier, each spindle having an eccentric crank pin and the crank pins engaging a drive member capable of gyratory movement relatively to the carrier and about an axis parallel to the axes of the spindles, in such a manner as to rotate the spindles, each crank pin being coupled to the spindle by a crank portion the axis of which is inclined at an angle of less than 90 to the axis of the spindle, and the spacing of at least some of the spindles being such that the crank portions of adjacent spindles are interleaved, the drive member being rotationally balanced by a balancing member arranged to gyrate 180 out of phase with the drive member, each member having coaxial therewith a circular and axially extending bearing surface, the radii of the two surfaces being such that one surface engages and rolls around the other, in epicyclic fashion, as the two members gyrate.

2. A multiple spindle head according to claim 1 wherein one surface is inwardly facing and encircles the other surface which faces outwardly.

3. A multiple spindle head according to claim 2 wherein the internal surface is on the drive member and the external surface on the balancing member.

4. A multiple spindle head according to claim 1 wherein the drive member is arranged to be gyrated by a shaft rotatable about a fixed axis and having an eccentric portion rotatable in a bearing on the drive member, and the balancing member is gyrated by a further eccentric portion on the same shaft which further eccentric portion is rotatable in a bearing on the balancing member, the two eccentric portions being displaced from one another by 180.

5. A multiple spindle head for a drilling machine comprising a carrier, a plurality of spindles rotatable in bearings in the carrier, each spindle having an eccentric crank pin and the crank pins engaging a drive member capable of gyratory movement relatively to the carrier and about an axis parallel to the axes of the spindles, in such a manner as to rotate the spindles, each crank pin being coupled to the spindle by a crank portion the axis of which is inclined at an angle 0 of less than to the axis of the spindle, and the spacing of at least some of the spindles being such that the crank portions of adjacent spindles are interleaved, there being means for preventing rotation of the drive member while it is gyrating, which means comprise at least one intermediate member connecting the drive member to said carrier, the intermediate member being restrained for movement relatively to the carrier in one direction only, normal to the axis of gyration, and restrained for movement relatively to the drive member in a direction at right angles to said one direction.

6. A multiple spindle head according to claim 5 wherein linear bearings are provided to permit movement of the intermediate member in the two said directions.

7. A multiple spindle head according to claim 6- wherein the intermediate member has a first groove which registers with a groove on the carrier, the two registering grooves locating a plurality of balls between them, and a second groove, at right angles to the first groove, which second groove registers with a groove on the drive member, the two registering grooves locating a plurality of balls between them.

8. A multiple spindle head according to claim 7 wherein there are provided a plurality of parallel grooves on the carrier and on the drive member, registering with corresponding grooves on the intermediate member.

9. A multiple spindle head according to claim 1 wherein each spindle is provided with a drilling tip which is separately formed from the spindle and is engageable with the spindle, the engaging portions of the spindle and tip being formed with mating surfaces inclined to the longitudinal axis of the spindle, and the spindle and tip being tightly embraced by a supporting sleeve at the junction between the mating surfaces.

References Cited UNITED STATES PATENTS 404,364 5/1889 Richards 77--7l 1,452,921 4/1923 McLellan 7722 1,870,391 8/ 1932 Stimpson 7723 2,972,914 2/1961 Lanier 7722 FRANCIS S. HUSAR, Primary Examiner US. Cl. X.R. 

